This paper studied the main factors which affected the degree of hydrolysis of CGM hydrolyzed with Alcalase protease.The results showed that enzyme concentrate was the main fac-tor,substrate concentrate and temperature in turn,pH was the last.The optimum conditions:E/S2.5%,5%,temperature 50℃,pH8.5.Under this condition,the CGM was hydrolyzed for six hours,DH was 28.53%.With prolong of time,the DH changed little.